A standard metered-dose inhaler, such as sold under the trade name "FLOVENT" by GlaxoWellcome, "PROVENTIL" or "VANCERIL" by Key Pharmaceutical, or "AEROBID" by Forest Pharmaceuticals, comprises a small pressurized medication-filled cartridge and a holder formed with a short tubular mouthpiece. After shaking the device the mouthpiece is inserted into the mouth between the lips and teeth. Then the patient exhales deeply to empty his or her lungs and then takes a slow deep breath as the cartridge is actuated to release a puff of the medication that is then drawn down into the lungs, normally to apply an antiinflammatory agent to them.
Such a system is extremely effective only if used perfectly. A particular problem is that the medication must be taken deep into the lungs, so that the lungs must be as empty as possible before aspirating the medication. These devices are, however, invariably being used by those suffering from breathing difficulties who are in fact often gasping for breath when the device is being used so that getting the procedure correct is a problem, in particular for children.
This has led to the development of aids that are used with an inhaler. U.S. Pat. Nos. 5,855,202 and 5,012,804 describe such a chamber that has a rigid cylindrical compartment provided at one end with a tubular extension serving as mouthpiece and of substantially the same size and shape as the mouthpiece of the inhaler. The other end of the compartment is provided with a hole into which the mouthpiece of the inhaler is fitted and a one-way valve at this other end allows air to be drawn into the compartment. Thus, after fitting the inhaler to the compartment, the user places the mouthpiece of the holding chamber in his mouth, actuates the inhaler to shoot a puff of the medication into the compartment, and then slowly inhales to draw in the charge from the compartment. Such an arrangement can even allow the user to draw in the medication in two breaths. It is known to provide a noisemaker or whistle in the wall of the compartment so that the user can test the seal around the inhaler by sucking on the mouthpiece to see if the whistle sounds. If it does not, there is a leak.
The disadvantage of these known systems is that they still require the patient to fully empty his or her lungs before aspirating the medications. It is very difficult for many people, in particular those with breathing difficulties, to exhale deeply and then not take in any more air before using the device. Usually as the mouthpiece of the holding chamber is inserted into the user's mouth, a short breath is stolen.